Free-standing nanoporous nickel (np-Ni) ribbons were directly synthesized by dealloying Mg90-xNix Y-10 metallic glass ribbons in citric acid aqueous solutions under free conditions. Due to the amorphous nature of the Mg90-xNixY10 precursors, the as-dealloyed samples exhibit a uniform nanoporous structure with the ligament size of similar to 7 nm. Effects of alloy composition, leaching time, and acid concentration on the resulting nanoporous microstructure were discussed. The lower limit of Ni content in Mg90-xNixY10 precursors was identified to be 20%, below which the nanoporous Ni could not be formed. Besides, a linear relationship was established between the ligament size and the leaching time on a logarithmic scale. The ultrafine structure of the obtained np-Ni was associated with the stabilizing effect of citric acid. The as-dealloyed samples with the naturally formed oxide surface of NiO were directly examined as binder-free electrodes for high-performance supercapacitors. (C) 2017 The Electrochemical Society. All rights reserved.